Somewhere on this site are the sales brochures, parts list, and info about the interior options. Takes some leg work. But what isn't around/couldn't find is the chart as to what combos they offered with the seat cloth or were available/sold. So you have to go to pictures, etc. I saw one "ivory" '48 or 49 sedan for sale about a year ago in CA and it had the plaid vinyl seats. Do not know if ext. color was orig. Another in NJ had the brown tweed which seemed to be prevalent based on the number of pictures I saw.
I even asked one car dealer to take an interior shot for me. You can also go to the PAC roster keepers, but unless they have or know of one like yours, it wasn't as helpful as I expected.
Some of the common interior items like the knobs, escutcheons, etc are "ivory" so it matches with a lot of colors and the "wood grain". I was told but never verified the 23 headliners were one color but that didn't seem to be the case nor matched the cloths. Good luck. It'll come down to cost, taste, and preference unless you have swatches to match.

I wouldn't recommend to pull the front clip until you see if it runs. It's not that difficult to work on the 8, if I could do it. If you jump into a pile of parts, and it doesn't run, what are you prepared to do?
Also, need a space and means to catalogue, store, and protect those parts. The car serves that function assembled.

Of course, I can't say this, it violates the "rules", so a little mouse told you. The non-PC "truth" isn't permitted to be told either these days. Chinese firedrill, cluster, you name it...
Ever since they came up with this global warming potential(GWP)and ozone depleting potential(ODP), the refrigerant game has been thrown into a decades long tail spin. The protocol had all the original and replacement compounds phase out dates and when the time for 134a had come up, "they"* decided 1234yf would be next(they're running out of alternates.) Appears Mercedes did more testing, subsequently, after it was "approved" but known to be slightly flammable but not bad enough to not use in 2013 and later models. The results were it decomposed to TFA trifluoroacetic acid, during spray on a hot engine which caused fire and etched the windshield. (I used to make solutions of TFA for pyrolytic glass coating - no surprise here)
So the "new" compound on the market is 1234ze (isomer) which is non-flammable, but also contains the perfluoro (PF) group that gives great stability. The EPA made everyone eliminate PFOA which was in Teflon for bio accumulation reasons even though no effects were seen. Well, we'll wait and see if they find the ze in people next. Apparently there's some reports of worker health issues with the 134a lubricant as well.
So I wouldn't use any of the modern compounds in a classic, aka in govt as a "clunker". R-12 is/was still being produced by the Chinese, who were somewhat exempt from the protocol the US bides by where it is "banned" but can be used(?). So I'd get me some and store, if I had R-12 A/C in my car. If was converted, I'd stock some 134a or one of the blend substitutes(400's numbers).
* - mostly the producers working with the users and seeking EPA guidance as it never really approves anything but bans stuff. EPA wants everything as safe as water but don't want to you to use water as it would be a "pollutant" then. At least that's one circular logic extension.

Restore to what(level over what time)? It's a "it depends" question you have to answer first. They're only original once. Best to start with a complete original condition car, if possible. Depending on how good it is will help decide how far you go.
How many times have you seen ads for "parts cars" for a few thou $ and it says "needs full restoration"?
Most won't command the post restoration value, so what's the point? It's a losing proposition(aka labor of love) mostly. Some of these "can't" be done and some parts can't be found so that means making them or having them made. {Check the rubber mat story] It takes a lot of skill and equipment that the average person doesn't possess or have access to. To get it done by others adds a good percentage to cost. I don't rule out ingenuity, but it's a bit wishful.
Everyone has their own methods. Some disassemble, blast everything, and start back. It's a time vs cash flow and manpower exercise mostly. If you tinker like most of us, you take your time. If you want Pebble Beach winner you farm it out to those shops.
The reality TV shows are distorting reality. Foose doesn't do Packards in a week!
They call it "ground up" because that basically covers it, you have to get it down to the last nut and bolt, the frame is left, get that straight, and go up from there. But there's alot of steps in there both taking apart and cataloguing, repair/replace, researching, procuring, mechanical, electrical, interior, body work, paint, assembly, etc. You have to fit and refit a few times during all that. It's project management by systems.
Reality check; your looking at ~$15K+ and a year just to do high quality chrome on that custom. The market value is not much more for a full restored car.

Troubleshooting 101: Eliminate the obvious first.
Changes: head, washers, different gasket than original, condition of the parts.
Any time a possibility for mismatch, check and recheck the fitment.
Verify the gasket fits the block and the head and has the right dimensions. Recheck the head to block fit. Examine the gasket to see where it compressed or did not.
Also, where it leaked should tell you the path of the fluid, how it got from the water side to the outside or inside. Concentrate on those areas for fitment.
Then go to proper sealing techniques.
Depending on the washer hardness, making it thicker may require more torque if the washer deforms more. Use at least same grade as the nut, grade 5, preferable 8. If you used low grade washers or made from soft metal they may not transmit all the torque properly. What you read on the torque wrench is the force applied, not what the force did or how much actually went into tightening.

Measure the ends of the rocker panel/door jam from the SS trim to the outer edge and see if steel is parallel or tapered. The mat edge should follow the panel edge and fit tight to the trim piece. There's some float in the clips which you won't have with velcro but can adjust fit to even out reveal.
On my 23rd series 2 dr drawing ribs are parallel but the rubber edge is tapered as is the steel and is 1/4" wider on one end. One end is cut on taper, other is straight. These mats are a lot longer, ~45", so 1/8" might be about right for 4 dr.

The ads are replete with fiberglass projects that were started, weren't completed, and owner wants their money out but won't get it because the finished cars never bring the bucks the steel ones do. So it's about the same odds as gambling.
I'd only do it if I lived in snow or ocean country and wanted to drive year around in the salt.

Without pictures, and doing most yourself, I'd say you're in the ball park to get it to the road but could be 30-100+% above depending on interior and chrome and some other factors. Alot depends on the time frame. Can you wait or want it bad now.
So before you go down that path and fork over, think long and hard! You won't have that luxury again once it commences.
The body/paint work is not that difficult but time consuming and requires a good eye, tools and/or access to services, and knowledge. Without those, it'll reflect it or ruin something requiring a do over.
Be prepared to either own it a long time or take a hit to the wallet at sell time. Sometimes wants are not what they're cracked up to be and turn into nightmares for rushers, faint of heart, or weak of mind.
The market does not support the increasing cost of restoration. You're better off paying for one a good one at auction but preservation suffers that way.
"Fell into your lap" sounds like a "moment of weakness", but we all have those.

Caveat Emptor.
A fool and his money...
History is replete with it.
Mostly the unknowing hoping to sell to the unknowing / unsuspecting as the above knowledgeable comments prove. Human perception of "value". In engineering, value equals function over cost, nothing more.
ps: I tried to get a non-working NOS antenna for my Cad off an "ebay" inheritor. They were asking alot more than any rebuilt (which works), reason was not an option because the decedant had told them it was "valuable", and they emotionally refused to budge on price. So I hope they or the new owner enjoy looking at their priceless non-working antique... I got mine fixed for cheap. Those parts usually hang around a long time, then they sell them cheap to a bargain hunter or throw them out. The unfortunate part is alot deteriorate do to mishandling in storage. I know of a desirable car that's been sitting out for more than 5 years - that I've known. I tried to buy it > a year ago, but the owner won't part with it, is "collecting" and it's gone worthless sitting out. Rare, in itself, only has great value when owner is willing to sell, someone wants or needs it and is willing to pay the great price. Otherwise, it's either junk or museum eye candy - pay a cheap price to look - at best.

Disc brakes are nice but alot of the period stock wheels won't work with them. The conversion guys don't like to tell you that before you buy them.
So if you change, you need to check, you may not be able to use the stock rims/hubcaps. I had to go dual master only to retain the stock rims on my Cad. Then you have to be concerned with the wheel cylinders and the added pressure. I found the post war stock Packard brakes stopped very good for being manual brakes but at higher HP in the later models, they may suffer.